Control by temperature sensitive gas bleed



Jan. 3, 1967 L. v. MCCARTY ETAL 3,295,586

CONTROL BY TEMPERATURE SENSITIVE GAS BLEED 3 Sheets-Sheet l Filed OCT.. 26. 1964 S Y Y RWA e OAC n TCN. R Neu w WMDW.. mvJ. .A mm .L LR

Jan. 3, 1967 v, MCCARTY ETAL 3,295,586

CONTROL BY TEMPERATURE SENSITIVE GAS BLEED Filed Oct. 26,` 1964 3 Sheets-Sheet 2 Mecuamcm.,

THaRMosTn-r (NVENTORS Louaoes V. MCARTY BY Roywf ATTORNY Jan 3 1967 l.. v. MCCARTY ETAI. 3,295,585

CONTROL BY TEMPERATURE SENSITIVE GAS BLEED Filed Oct. 26, 1964 5 Sheets-Sheet 3 Fxe. L

lNvENToRS r LouRbes U. MCAR1Y ROBERT .DLZK /5/ f 7/ AroRNEY United States Patent O 3,295,536 CONTRGL BY TEMPERATURE SENSITIVE GAS BLEED Lourdes V. McCarty, Milwaukee, and Robert 3. Duncan, Delaiield, Wis., assignors to Controls Company of America, Melrose Park, lll., a corporation of Delaware Filed Get. 26, 1964, Ser. No. 496,233 12 Claims. (Cl. 158-136) This invention relates to detection of heat for control purposes.

The following description is largely devoted to detection of a gas llame and application of the detection apparatus to gas control systems. The invention in its ybroader aspects is, however, applicable to detection of heat or a flame in other environments such as sensing an oil burner llame, etc. in the gas art the flame detectors are largely the thermocouple-electromagnet type and in other fields various other sensors are used. The present sensor is lessexpensive and faster acting than other known sensors.

The principal object of this invention is to provide a fast acting reliable flame sensing device.

A further object of this invention is to apply such a device to a safe and reliable control system for gaseous fuels.

Another object is to adapt the control system to either a standing pilot -or electric ignition.

Still another object is to provide a simple pilot burner which also functions 4as part of the sensor.

The present invention hinges upon the flow of =a gaseous medium through a conduit having a restriction on both the inlet and the outlet so that application of heat to either restriction will change the static pressure in the conduit with the pressure change being employed to eect a control function.

Other objects and advantages will be pointed out in, or be apparent from, the specification and claims, as will obvious modifications of the four embodiments shown in the drawings, in which:

FIG. 1 is a schematic showing of the basic sensor and control;

FIG. 2 shows an application of the concept to a gaseous fuel control system and includes an arrangement for rendering the sensor free from adverse effects from inlet pressure variation;

FIG. 3 shows -a further modification of the sensor system to fail safe if the restriction should plug or become further restricted; and Y FIG. 4 shows `a further modified system, this system being preferred.

Referring now to FIG. 1 which illustrates the basic concepts involved here, this ligure shows a conduit C1 leading to a second conduit C2 through a restriction R1. There is a further restriction R2 on the outlet of conduit C2. Gas will flow in the direction indicated through C1, R1, C2, and R2 in series. The gas may be a gaseous fuel or can be air -or any other gas or fluid which obeys the gas laws. The pressure in the two conduits C1 and C2 are respectively designated P1 and P2. It should he noted that for control purposes of the type here under consideration we are preferably dealing with low pressures, that is, measured in inches of water although with some modification to the applicable formulas higher pressures can, no doubt, be employed in the same system. The crosssectional areas of the conduits C1 and C2 are large compared to the cross-sectional areas of R1 and R2 and the latter cross-sectional areas may be designated A1 )and A2.

A conduit 16 leads from conduit C2 to the housing 12 whereby the static pressure P2 in conduit C2 may be applied to the underside of diaphragm 14 which is biased by spring 16 so as to move the bridging member 18 away ice from the contacts 20, 2l). With this arrangement if the pressure increases below diaphragm 14- sufiiciently to overcome the spring 16, then the diaphragm will move upwardly to bring the contact bridging member 1S against the switch contacts and close the switch. This is primarily for illustrative purposes to show a control device responsive to the pressure acting against the diaphragm.

The essence of this invention lies in the fact that if heat is applied to either restriction R1 or R2 with a gas flowing through the conduits, the pressure P2 in conduit C2 will be affected. lf heat is applied to R1 this will cause pressure P2 in conduit C2 to decrease. lf heat is applied to R2, P2 will increase.

For control purposes it is preferred to operate with the increase in pressure and, therefore, the following is directed to the :concept of applying heat to R2 to thereby cause an increase in P2 but it should be remembered that heat can be applied to either R1 or R2. By application of the basic gas laws and those laws relating to low pressure gas flow, various important effects resulting from application of heat to R2 can be calculated and laboratory tests verify these calculations. In these tests and in the application of this basic concept to control systems we have dealt with a gas flame applied to R2 which heats the fluid in the restriction to 2l20 R. as opposed to the roorn temperature of 530 R. The application of the basic gas laws demonstrate that the effective area of R2 when it is hot is T Ain: 'AQo Thus, the effective or apparent area when restriction R2 is hot is A211=V2 A2C.

The static pressure in conduit C2 when R2 is not heated but is at room temperature can be shown to be For a practical example we may select A2=1.2A1 and solving the foregoing equation give P2C=0-41 and P2H=0.736. From this it can be seen that the application of heat to R2 results in a substantial increase in P2 and it is this increase in pressure which can .be used to effeet the control function in the arrangement shown in PEG. l. ln other words, when the pressure P2 in conduit C2 increases upon-application of heat at R2, this will ybe suihcient to lift diaphragm 14 t-o close the switch contacts 2d. This, then, represents the basic concept and application to a control system.

The cross-sectional area A2 of restriction R2 can be selected in various ratios with respect to the area A1 of R1. These may be plotted to show the variation of P2 with respect to P1 for different values of A2 with respect to A1. Such a graph is helpful in establishing the dcsign parameters to accomplish given purposes,

Consideration of FIG. l will readily make it apparent that the system is subject to improper operation if the pressure P1 is subject to variation. This, of course, would result in P2 being varied also and if the P1 variation was sufficient, then this variation by itself could be suicient to operate the pressure responsive control. This can be overcome by regulating the pressure at C1. Another way to overcome this problem is shown in FIG. 2 and before describing this arrangement in full detail it would be best to confine the consideration to the basic system and the manner in which the inlet pressure variations can be overcome. Iny graphing the cold and hot P2 curve it is then convenient to take a mean curve which can be used in selection of diaphragm sizes as has been the case with respect to FIG. 2. In FIG. 2 there is a housing 22 having an inlet 24 leading to the chamber 26 below diaphragm 28 which is ganged or serially connected with diaphragm 30 to jointly control valve 32. It will be noted that here we are using a valve as the control device vrather than the switch shown in FIG. 1. means of calculation the area of diaphragm 28 has been selected to be 0.572 times the area of diaphragm 30 so that the operating force acting on valve 32 in either the closing or opening direction will be the same if area A2 of R2 is again 1.2 times A1. With these selected values and with diaphragm 30 being taken as unity and P1 being taken as unity it can be shown that the opening or closing force (R2 hot or cold) will be 0.0058 pound. Changing By means of a graph or by the pressure or the area of the diaphragm 34) will not alter Y this arrangement except as to value of the ultimate opening or closing forces. Now, then, it will be appreciated that when the valve 32 is open the pressure under diaphragm 28 will be the same as the pressure at C1. In other words, it will be P1. The pressure above diaphragm 30 is derived from C2 and, hence, is P2. If R2 is hot the force on diaphragm 30 will be sufficient to hold the valve open. If R2 is cold the pressure below diaphragm 2S Will be sufficient to close the valve. It will be appreciated that by selection of the size of diaphragm 28 with respect to diaphragm 30 so as to obtain equal forces with changing inlet pressure the variations in inlet pressure will not have any effect on the position of valve 32 since these will be reiiected as variations in P2. Therefore, this arrangement will control properly Without regulating the inlet pressure.

An important aspect of this FIG. 2 should now be observed and that is that R2 is in the form of a capillary tube turned back on itself so that the issuing gaseous Yfuel may be ignited to heat the restriction R2. YThis is a very convenient way to obtain the heat and, of course, this llame can now function as a pilot burner.

Further reflection upon FIG. 2 will readily demonstrate Vthat when valve 32 is closed there would be no way to open the valve merely by heating restriction R2. Therefore, there is provision for y:a start valve 34 -in the bypass 36 to supply inlet fuel directly to C1. Valve 34 would be opened to permit ignition 0f the flame atV R2.

This leads us to the further advantage of this system inA Similarly, should the pilot bel 4 inlet pressure is acting on the underside of the diaphragm valve except for the area occupied by the valve seat 60.

A spring 62 also urges the diaphragm valve closed and this operation of the main valve 52 upon opening of the.` Now, then, should the pilot go4 out to allow R2 to cool, the safety valve 32 will closeas i thermostatic valve 50.

previously discussed. This closes the bleed from above the main valve and allows the pressure to build up above the main valve S2 until it seats. Therefore, this system is a completely safe arrangement whereby the ow to the main burner will be cut oli if the pilot burner isextin-` guished. If the pilot burner has been extinguished with the thermostatic valve 50 in its closed position it will be obvious that opening the thermostatic valve cannot drop the pressure above the main valve 52 and, hence, the main valve will not open.

In each of the foregoing modifications there is a prob-k lemwith respect to the sensing means becoming unsafe should the restriction R2 become plugged or partially restricted since this would tend to increase the P2 pressure operating to hold the valve open. Y an arrangement which would be applicable to the sensor arrangement of FIG. 2 but which will secure closure` Y of the system if the restriction R2 becomes plugged. To

to a complete control system as shown in FIG. 2, this Y control is provided with a gas cock 38 which is provided with the suitable cutouts 40, 42 for respectively directingy flow to the pilot burner and to the main burner. The pilot ow passes through filter 44 and a restriction 46 and then goes to inlet 24 or the bypass line 36 and a branch 48 leads to the thermostatically operated valve 50. If the thermostatic valve 50 is closed and the gas cock 38 is positioned to allow flow to the underside of the -main diaphragm valve 52 there will be some flow through filter 54 and restriction 56 through the conduit 58 to the space above the diaphragm 52. This, therefore, places theinlet pressure above the diaphragm valve 52 and the same facilitate the comparison of these arrangements similar,

numerals are used to designate the housing 22, the inlet 24the diaphragm 28, the upper diaphragm 30, and the control valve 32, as well as the conduits C1 and C2 and the restrictions R1 and R2. in the same manner as described with respect to FIG. 2.v The arrangement of FIG.V3 employs .a second control valve 62 in series with valve 32.y This valve 62 is carried Yby a diaphragm 64 which is ganged lor in series with diaphragm 66,- the underside of which will be exposed to pressure P2 while the upperside of diaphragm 64 is exposed to pressure P1. The area of diaphragm 64 is selected as .8 of the .area of diaphragm 66 with the result the force derived from P1 acting on diaphragm 64 is greater than the force derived from P2 acting on 66 and the lower valve 62will be inactive 4(open) until sufiicient obstruction of R2 causes P2 to rise to close the lower valve 62. This, of course,will cause the reduction of P1 and P2 with the result that the P2 force acting on the upper diaphragm 30 will drop and allow the inlet pressure to act on diaphragm 28 to close valve 32. Of

course, with the total shutdown the P2 pressure falls toA In order to zero and the lower valve 62 will re-open.

re-establish the flow now it would be necessary to resort to a start valve arrangement such as shown in FIG. 2.

The .arrangement shown in FIG. 4 provides another method of shutting off flow in the event the restriction R2 becomes plugged or restricted. This figure addi-` tionally shows the relationship of the new control concept to a complete control system for a gas burner and, as will be apparent hereinafter, this system is readily adaptable to Voperation either with a standing pilot or with electric ignition.

In FIG. 4 `the inlet 68 leads to the underside of theV 84 to conduit 86 which leads to the space below dia-` FIG. 3 shows All of these parts operate phragrn 88 which is the control diaphragm affected by the pressure increase incident to the heating of the restriction R2, as above mentioned. This diaphragm carries valve 90 and the ow past valve 90 is led to the conduit 92 to the cut-out portion 94 in the gas cock 96 so that it can be reintroduced to conduit 98 and led to the chamber C1 below the diaphragm valve 160. This diaphragm valve is the valve which will close on its seat to shut oif How in the event the restriction R2 becomes unduly restricted or plugged. The method of operation of this valve will be described more fully hereinafter. Flow to the pilot then proceeds from chamber C1 through restriction R1 to chamber C2 and thence to restriction R2 which is again turned back on itself so that the gas coming from the restriction can be ignited to operate as a pilot and also to heat the restriction R2 to obtain the pressure increase in accordance with the basic concepts of the present invention.

A lateral conduit 102 leads from the chamber C2 through the restriction 104 to be communicated to the space above control diaphragm S8 and also to the space above diaphragm 100. If the shut-ott valve 9i) is closed it will be obvious that the pressure acting below diaphragm 88 will hold the valve closed and there is no way to obtain flow to restriction R2. In order to accomplish this some means must be provided for either bypassing the valve 9i) or for opening the valve 90 on a temporary basis. The latter arrangement is shown in the present drawings where a reset plunger 166 can be depressed against the spring 108 to act against diaphragm 110 to, in turn, depress the plunger 112 against the bias of its spring 114 to act against the top of diaphragm 83 and open the valve. It is clear that the diaphragm 11i) is merely employed as a means of sealing the reset mechanism and other arrangements could be used. It shoul-d also be clearly understood that the reset 196 should be interlocked with the gas cock so that it can be operated only lwhen the gas cock is in its pilot position, that is, in position to block ow to the main burner 116. To permit the reset to be operated when the gas ow can occur through the main burner could, of course, be quite dangerous. Such interlock is well known in this art and need not be shown here.

Upon operation of the reset 186 to open valve 90 gas ows through passages 92 and 98 to the underside of valve diaphragm 100. This pressure would lift the valve against the bias of spring 118 to permit flow through R1, C2, and R2 and allow the burner to be ignited. The reset should be held depressed to retain valve 90 open until R2 is hot and P2H has been established above diaphragm 88. If the restriction R2 becomes unusually restricted or plugged, P2 will increase and build up on top of valve diaphragm lili) to force the valve closed which, of course, results in dropping P2 above diaphragm 88 allowing the pressure under diaphragm 88 to close valve 90. The normal safety function of this device, of course, is the same. If the pilot burner goes out, R2 will cool causing P2 to drop and allowing the pressure on the underside of diaphragm S8 to close valve 90.

Now continuing with the description of the entire control system, it will be noted that gas flowing through the filter can, in addition to passing through the regulator valve 76, also pass through the restriction 129 and to the space above the main diaphragm valve 70. Conduit 122 leads from this space up to chamber 82 and has a valve seat at its upper end with which the diaphragm valve 124 of the servo regulator can cooperate. Valve 124 is carried by diaphragm 84 which also carries a second valve 128 which can cooperate with seat 130. Valve 128 when seated prevents ow to the main burner if the diaphragm 84 should leak. The space above diaphragm 84 communicates through conduit 132 with the main burner line 134 downstream of the main valve.

For operation of the entire system with a standing pilot, a thermostatically operated valve will be located at 'the point A and the conduit 122. It a valve so located is closed it will be obvious that line pressure can build up through the ow path 72 and lter 74 and restriction 120 to apply line pressure above diaphragm 170 which, together with the force of spring 135, will seat the main valve. Now, then, since the main valve is closed, there will be no pressure downstream of the main valve and, therefore, there will be no pressure communicated through conduit 132 to the space above diaphragm 84. Under these conditions lthe force of spring 136 acting in they upward direction on the diaphragm 84, together with the gas pressure acting below the diaphragm 84, will overcome the upper spring 138 and close valve 128 against its seat.

Now if the valve located at point A is opened, whether by an electrical or mechanical thermostat, the pressure existing above diaphragm 7i) can rapidly drop since there is a direct iiow path into the chamber 82 and flow through the restriction cannot make up for this pressure drop through the relatively free or open path. Therefore, the pressure will drop rap-idly and allow valve 70 to open. As soon as valve 70 opens the pressure will build up downstream of the main valve and will be communicated through conduit 132 to move valve 128 downwardly and then act on the diaphragm 84 to regulate movement of valve 124 with respect to its seat. When the valve located at A opened and the pressure above the main valve was released into the chamber S2 the effect would be to normally raise the regulated pressure supplied to the pilot burner. However, the pressure regulator 78 will immediately sense this and reduce the ow via that route and there is no adverse effect sufficient to close valve 90. The springs 136 and 138 acting on the servo-regulator dia phragm 84 are selected so that the main burner gas pres Vsure existing in line 134 will so regulate the bleed through line 122 from the space above the main valve 70 that the pressure in line 134 will be regulated at a desired value. In other words, as the pressure in line 134 tends to increase, the pressure above the servo-regulator diaphragm 84 will tend to increase and move the valve 124 closer to its seat and reduce the bleed from the space above the main valve which will allow the pressure to build up above the main valve and partially close the main valve to regulate the pressure.

When the thermostatic valve located at A is closed, the pressure above the main valve will immediately build up and cause the main valve to close. If the pilot ilow is shut off either by reason of the pilot going out causing closure of valve 9i) or because of plugging of t-he restriction R2 causing closure of valve with subsequent closure of valve 9G, then there is no escape for the gas above the main valve 70 and, therefore, line pressure will rapidly build up on top of the main valve '70 and close oft' the main va-lve even though the valve at A may be open. Therefore, this arrangement is completely safe. After such a complete shutdown it will be necessary to re-establish the pilot and, as noted above, it is preferred that the reset be interlocked with the gas cock so that ilow to the main burner cannot occur during the ignition of the pilot. With the gas cock 35 being located downstream of the main valve 7d, there cannot be any sudden rush of gas to the main burner when the gas cock is opened to allow such flow since this permits pressure to be maintained in the main valve chamber when the cock is positioned to prevent flow to the main burner.

If the system is to be used with electric ignition there is, of course, no desire for a standing pilot so that the pilot burner playing on R2 would not be necessary. Under these circumstances the R2 operation is employed lto prove ignition and to shut down gas ilow if ignition fails to take place. For an electric ignition system the thermostatic valve would not be located at point A but instead would be located at point B. If we assume a valve located at point B and that this valve is closed, it will be obvious there is no pressure acting under safety diaphragm S8 to hold this diaphragm in the up position closing valve 90. 1 Therefore, valve 90 will be open. Valve 100 will be closed. Now if the valve at point B is opened, the sudden application of pressure to the underside of diaphragm 88 would tend to close valve 90 and prevent ow to the pilot burner. This is prevented in the present arrangement by the provision of the restriction 104 so that when the valve B is opened and the diaphragm starts moving up it must exhaust the gas accumulated above the diaphragm 88 through the restriction 104 which introduces a time delay in the operation sufficient for gas ow to get established at the pilot and for the pilot to heat R2 causing P2H to build up and hold the diaphragm in its running position. Of course, gas under diaphragm valve 100 will open that valve so there is no problem getting past that point.

With valve B closed line pressure will now also be acting on top of the main valve to hold this valve closed. When the thermostatic valve opens at point B the pressure above the main valve can drop rapidly and allow the main valve to open so that While ow is being established to the pilot there is also flow established to the main burner where it Will be ignited by a spark or other suitable ignition device. Whether the pilot or the main burner is ignited, one will light the other and heat R2 and place the system into operation. Closure of the valve at point B Will, of course, cut olf supply of gas to the pilot and will also cause the line pressure to build up on the main valve diaphragm 70 to close the main valve. Now consider the abnormal situation of failure of ignition. If ignition fails to take place, the pressure above diaphragm 88 can bleed off through the restriction 104 and cause valve 90 to close, which will then shut down the entire system. If the flame has been established but for some reason goes out, R2 will promptly cool causing a drop in the pressure above diaphragm 88 which will allow valve 90 to close and this will then close the main valve by reason of causing the pressure build-up on diaphragm valve 70. Similarly, if the restriction R2 gets plugged, then the pressure will build up on valve diaphragm 100 to closethat valve and cause the drop in pressure P2 which will reflect in closure of valve 90 which Will then shut down the system. Whenever the systemishuts down by reason of the closure of valve 90, directly or indirectly, it will be necessary to either employ a reset such as 106 or to bypass the safety valve 90 in order to place the system back into operation. The reason for this is that if a shutdown occurs by reason of closure of valve 90 rather than closure of valve B, then line pressure will exist below the diaphragm 88 whereas with closure of valve B `no pressure exists below the diaphragm 8S.

The foregoing control system assumes that the electric ignition device would continue to operate all the While the main burner was in operation. It Would, of course, be a simple matter to de-energize this ignition system with the use of a device similar to that shown in FIG. 1 except that in the arrangement of FIG. l a circuit is completed upon heating of R2. Here lit would be desired to break the ignition circuit upon movement of a diaphragm upon application of P2H to the diaphragm. With such an arrangement, when the burner is shut down, either thermostatically or through operation of one of the safety devices, the ignition circuit would be completed and again ready for operation.

Another point to be noted is that the restriction 104 has .a safety function (in addition to the time delay feature for electric ignition) in that it affords a greater restriction to gas tlow than does the restriction 120. Therefore, if either diaphragm 88 or 100 should leak when the system is shut down, then restriction 104 will prevent l-oss of pressure above the main valve 70 and insure the main valve being closed. If the restriction afforded by 104 was not greater than the restriction 120, a leak at either 88 or 100 could cause the main valve to open.

While not considered as practical, this theory could be applied to heating one portion of a capillary tube and sensing a change elsewhere in the tube.

Although four embodiments of the present invention 1. A control for gas burners comprising, a pilot burner,

fuel supply means for the burner including rst and second restrictions having a conduit therebetween, a safety valve controlling the supply to the first restriction, the pilot burner being positioned to heat the second restriction, means controlling the valve in response to the change in pressure of the gas owing through the conduit in response to heating of said second restriction, means for establishing fuel flow to the first restriction and burner for burner ignition purposes, a pressure regulator in the fuel supply means ahead of the safety valve, a second safety valve in the fuel supply means and responsive to an abnormally high pressure in the conduit to stopy flow to the rst restriction.

2. A control according to claim 1 in which the sec-A ond safety valve is located between the first safety valve and the rst restriction.

3. A control according to claim 2 including a main burner, a main valve for controlling supply of fuel to the mainburner, a diaphragm for controlling the main` valve and having one side exposed to gas line pressure, a chamber on the other side of the diaphragm, a restricted connection from the inlet to the diaphragm chamber, an unrestricted connection from the diaphragm chamber to said fuel supply means downstream of the pressure regulator, a diaphragm operated valve regulating ow through the unrestricted connection, the last named diaphragm operated valve being responsive to the regulated pressure in the fuel supply means and to the pressure in the main burner supply downstream of the main valve.

4. A control according to claim 3 including a thermostatically operated valve in said unrestricted connection.

5. A control according to claim 3 including a thermostatically operated valve in fuel supply means ahead of the first safety valve and downstream of the junction of the unrestricted connection with the fuel supply means.

6. A contr-ol according to claim 5 including means for damping response of the pressure responsive `first safety valve controlling means whereby opening of the thermostatic valve will not close the first safety valfve` before affording the conduit pressure time to build up i incident to heating of the second restriction tothereby.

hold the valve open.

7. A control according to claim 6 including means for electrically igniting the fuel.

8. A control for gas burners comprising, a pilot burner, fuel supply means for the burner including first and second restrictions having la conduit therebetween, a safety valve controlling the supply to the first restriction, the pilot Iburner being positioned to heat the Vsecond restriction, means controlling the valve in response to the change in pressure of the gas owing through the conduit in response to heating of said second restriction, means for establishing fuel flow to the first restriction and burner for burner ignition purposes, a main burner, a main valve controlling supply of fuel to the main burner, a4 diaphragm controlling the main valve and having one4 side exposed to gas line pressure, a chamber on the other side of the diaphragm, a restricted connection from the.

inlet to the diaphragm chamber, an unrestricted connection from the diaphragm chamber to said fuel supply i means, a diaphragm operated valve regulating ow through the unrestricted connection, the `last named diaphragm operated valve being responsive to the pressure in the fuel supply means and to the pressure in the main burner supply downstream of the main valve.

9. A control device comprising, a conduit for a gaseous medium and having a restriction on its inlet and a restriction on its outlet, means for heating the medium owing through the outlet restriction, and safety means responsive to the change in pressure of the medium in the conduit resulting from such heating to effect a control function, means responsive to the supply pressure of the medium to the inlet restriction to oppose the response characteristics of the safety means to thereby reduce the effect of supply pressure changes.

10. A control device comprising, a conduit for a gaseous medium, spaced restrictions in the conduit, means for heating the medium owing through the restriction which is downstream of the other, a safety valve controlling ow through the conduit, means responsive to the pressure in the -conduit between the restrictions to hold the valve open in response to the pressure resulting from heating the downstream restriction, means responsive to the conduit pressure upstream of said other restriction to oppose action of the iirst named pressure responsive means whereby to offset the eiects of pressure variations.

11. A control device comprising, a conduit for a gaseous medium, spaced restrictions in the conduit, means for heating the medium ofwing through the restriction which is downstream of the other, a safety valve controlling liow through the conduit, means responsive to the pressure in the conduit between the restrictions to hold the valve open in response to the pressure resulting from 10 heating the downstream restriction, and means responsive to an abnormally high cond-uit pressure between the restrictions indicative of plugging of the downstream restriction to interrupt ow through the conduit.

12. A control for gas burners comprising, a pilot burner, fuel supply means for the burner including lfirst and second restrictions having a conduit therebetween, a safety valve controlling the supply to the tirst restriction, the pilot burner being positioned to heat the second restriction, means controlling the valve in response to the change in pressure of the gas flowing through the conduit in response to heating of said second restriction, means for establishing fuel ilow to the rst restriction and burner for burner ignition purposes, a main burner, a main fvalve controlling supply of fuel to the main burner, a diaphragm controlling the main valve and having one side exposed to gas line pressure, a chamber on the other side of the diaphragm, a restricted connection from the inlet to the diagram chamber, an unrestricted connection from the diaphragm chamber to said fuel supply means, a control Valve regulating tlow through the unrestricted connection.

References Cited by the Examiner UNITED STATES PATENTS 2,653,768 9/ 1953 Penn 15S-136 X FOREIGN PATENTS 1,137,512 1/1957 France.

85,149 4/ 1957 Netherlands.

FREDERICK KEITERER, Primary Examiner. 

1. A CONTROL FOR GAS BURNERS COMPRISING, A PILOT BURNER, FUEL SUPPLY MEANS FOR THE BURNER INCLUDING FIRST AND SECOND RESTRICTIONS HAVING A CONDUIT THEREBETWEEN, A SAFETY VALVE CONTROLLING THE SUPPLY TO THE FIRST RESTRICTION, THE PILOT BURNER BEING POSITIONED TO HEAT THE SECOND RESTRICTION, MEANS CONTROLLING THE VALVE IN RESPONSE TO THE CHANGE IN PRESSURE OF THE GAS FLOWING THROUGH THE CONDUIT IN RESPONSE TO HEATING OF SAID SECOND RESTRICTION, MEANS FOR 